Process for purification by crystallization

ABSTRACT

A process and apparatus are disclosed for the purification of multi-component liquid feed material having a crystallizable component employing a centrally-fed purification column substantially free of internal obstructions, a freezing chamber in communication with one end of the purification column, a melting chamber in communication with the other end of the purification column, and displacement means in the freezing chamber for passing frozen crystallizable component from the freezing chamber to the purification chamber and melting chamber.

United States Patent 1191 Filed: Feb. 22, 1971 Appl. No.: 117,526

Moyers, Jr. Mar. 12, 1974 PROCESS FOR PURIFICATION BY 2,922,701 1/1960 Ratje 23/273 CRYSTALLZATION 3,212,281 10/1965 McKay 62/58 3,261,170 7/1966 McCarthy et al.. 62/58 .[75] Inventor: Charl s ut y Jr-, 3,296,811 1 1967 $161161 62/58 Charleston, W. Va. 3,501,275 3/1970 Sailer et a] 23/273 Primary ExaminerNorman Yudkoff Assistant ExaminerR. T. Foster Attorney, Agent, or FirmGerald R. OBrien, Jr.

[57] ABSTRACT A process and apparatus are disclosed for the purificag 62/58 23/ 3 53353 tion of multi-component liquid feed material having a .crystamzable component employing a centrally fed 8 Field of Search 23/273 62/58 123 purification column substantially free of internal ob- 56] R f C1 d structions, a freezing chamber in communication with e erences l 8 one end of the purification column, a melting chamber UNlTED STATES PATENTS in communication with the other end of the purifica- 2,324,869 7/1943 Oman 62/58 tion column, and displacement means in the freezing 2,6 7 /195 chm i 23/ 7 chamber for passing frozen crystallizable component 2167mm 4/ Fmdlay 23/273 from the freezing chamber to the purification chamber 2,747,00l 5/1956 Weedman 23/273 and melting chamber 2,765,921 ll/l956 Green 23/273 2,862,797 l2/l958 McKay 23/273 3 Claims, 1 Drawing Figure ,{Il 1/ (-16 f /1 H1 52 w 20 I i 1? P 42 44-r 1 i If 46 1 PROCESS FOR PURIFICATION BY CRYSTALLIZATION The present invention relates to crystallization purification process and apparatus and, more particularly, to

such process and apparatus in a column-type system.

Heretofore, a number of systems have been suggested for the crystallization purification of multicomponent liquid streams. However, only two such prior systems of the column-type have been thought sufficiently practical to have been broadly utilized on a commercial or laboratory scale.

In one such system, an end-fed column is employed having freezing means positioned near the inlet feed end, melting means positioned near the opposite product outlet end hydraulic force pulsing means positioned near the product outlet end to transport solids.

In the other such system, a center-fed column is employed having freezing means positioned near one end of the column, melting means positioned near the other end, rotary and oscillatory conveyor means in the column to convey solids, with the purified product removed through the melting means and the filtrate removed through the freezing means.

It has long been realized that each of these systems presents serious problems for broad scale use. The former system presents the difficulty that it is unsuitable for total reflux operation which is often desired. In addition, since the solid 'phase is formed externally of the column, the internal liquid reflux in the column is essentially fixed by the thermodynamic state of the feed relative to the product stream. Consequently, product purity may be impaired because of the inflexible reflux limitation.

The latter system presents the difficulty that scale-up for commercial use is extremely difficult due to the mechanical complexity of the internal conveyor means employed within the column. No apparatus based on this system, having a diameter greater than 6 inches, is known to have been built during the approximately 10 years since the system was first disclosed.

It is, therefore, the prime object of the present invention to provide a process and apparatus for crystalline purification of multi-component liquid streams which are capable of utilization at all controlled reflux condi-' tions including full reflux and which are notsubject to mechanical complexity difficulties when scaled up to commercially useful sizes,

I Other aims and advantages of the present invention will be apparent from the following description and associated drawing.

In accordance with the present invention, a process is provided for the purification of multi-c'omponent liq-- uid feed material having a crystallizable component comprising: introducing said liquid feed material into an elongated purification zone substantially free of internal obstructions; passing liquid feed material from the purification zone to a freezing zone, positioned in communication with an end of the purification zone, to

freeze a component of theliquid feed material to the crystalline phase; displacing crystalline phase material from the freezing zone into the purification zone; maintaining a heated melting zone in communication with the opposite end'of the purification zone to re-melt the crystalline phase material passed into it; maintaining temperature balance on both the freezing and melting zones to produce a controlled reflux rate of crystallizable component through the purification zone, and withdrawing highly purified crystallizable component from the melting zone and the other components of the multi-component liquid feed from the freezing zone at a rate coordinated with the rate of introduction of liquid feed material and the temperature balance maintained in both the freezing and melting zones.

In accordance with the apparatus aspect of the present invention, apparatus is provided for the purification of multi-component liquid feed material having a crystallizable component comprising: a purification column having opposite ends and. being substantially free of internal obstructions for introducing feed material thereto and inlet means a freezing chamber positioned in communication with one end of-the purification column and having outlet means near the end thereof opposite said communication; amelting chamber positioned in communication with the other end of the column and having outlet means near the end thereof opposite said communication; and displacement means associated with the freezing chamber for passing frozen crystallizable component from the freezing chamber to the purification chamber and the melting chamber.

As employed herein, the term multi-component feed material denotes a liquid solution having a crystallizable componenflthe solution exhibiting either a eutectic or solid solution liquid-solid phase behavior. Such materials are well known to the art, para-xylene and meta-xylene being a typical example of the eutectic type, and naphthalene and fi-naphthol being a typical example of the solid solution type. A lengthy listing of i groups of illustrative systems of components is set forth in column 13, lines 25-74 of US. Pat. No. 2,854,494, which listing is incorporated herein by reference.

In general, however, the present invention is applicable to the purification of any material that has a welldefined melting point in the range of from C. to +250C., a range which would include most organic chemicals and exclude most inorganic chemicals.

Accordingly, as employed herein, the terms freezer," freezing and freezer means refer to the solid state crystallization in solution of the meltable component to be purified, upon cooling. The multicomponent feed material may also be an aqueous material, such as foods orjuices, which may be concentrated by the removal of water, or salt brines from which it may be desired to remove purified water.

It is to be noted that the multic0mponen t feed material" may constitute merely a binary system of components' or may constitute a system having a large number (i.e. 20).of components. The sole requirement is that the system is such that a solid phase is formed when the feed material is cooled to within the range indicated above.

, It is to be understood that the selection of the heatingv and coolantfluids employed is neither critical nor reas steam, air nitrogen, carbon dioxide, gaseous hydrocarbon, or the like.

In the appended drawing, the single FIGURE schematically set forth, in elevational view, crystallization eter Millipore perforated discs (300 micron diameter holes 6 percent open area).

In various embodiments of apparatus tested, l-inch diameter purification columns having lengths of 6- let port 50.

Purified product material is passed from the system through product outlet 52, while the other components of the multi-component inlet feed are passed from the system through overflow liquid outlet 54. Thermocou- 5 ples 56 are positioned at des1rable temperature measurement points as desired.

The solid phase is constrained within the column system by screens 58 positioned near the base of heating means 40 and the lower face of porous piston 38.

h The purification column section 20 is free of internal members and presents a region of continuous liquid phase material in contact with a discontinuous phase of solid (crystalline) material.

In 40-inch long, l-inch I.D. over-all column system, having stainless steel jacketed freezer and heater sections, flat, Teflon scraper blades and multi-drilled Teflon piston, typical scraper and piston operation were as follows:

Stroke Rate: 30 per minute Stroke Lengthaits-inch Scraper Speed: 120 RPM The screens58 which were employed to constrain the solid phase in the column system were l-inch diampurification apparatus representing one embodiment of 5 i lzihchesahd lsihches were h y eaCh the invention 1n con unction w1th 6-1nch heater and 6-1nch freezer As there shown, multi-component feed material to b sectlohs- I g I crystallization purified is passed from storage tank 10, hi P In accordance wlth the Invention, i through line 12, by pump 14, to crystallizationh to the f y w t0 t qpurification column system 16. The material enters col- 10 helght Indicated at 60 In the g, with the umn system 16 through inlet means 18, positioned genheater off and freezer and t P Q F Outlet losed n between column Section 20 and communicating and overhead outlet open until a sollds Inventory 1s esfreezer means 22. Freezer means 22 comprises an outer tablished. The heater is then turned on and operation cylindrical sleeve 24 concentrically positioned about continued until desired remelting equilibrium 1s estaban inner li d i l member 26 to form an annular lished under total reflux conditions. Thereupon, steady coolant passage 28 between coolant inlet port 30 and state conditions are attained in which discontinuous coolant outlet port 31. solid phase is built up in the continuous liquid phase of izs sbciated with freezer means 22 and the region 37 the Purification chamber- Thereupon, the inlet feed, (optional) above it is a flat, internal wall scraper 34 for the Product Outlet, the overflow outlet, the h at r keeping the internal side walls clear of crystal formaand freezer Controls are balanced to Obtalh the i w ll scraper 34 i d i i rotary d ill trolled reflux conditions required for the desired purifitory manner by drive shaft 36 which also actuates pis- Canon operation. ton 38 (having porous drill ports 39) in a similar man- The followmg examples set forth data for the purifinet to pass crystals from the freezer means to the colon of lde from a binary eutectic system of umn Section 20 v acetamide and water. Acetamide of greater than 99.9

Heating means 40 are positioned in communication percent purity was produced continuously from soluwith column section 20 at its opposite end. Heating tions containing 0.03 to 0.10 mass fractlon water.

-- TABLE Feed Product Example No. Rate cc/hr Composition Rate cc/hr Composition Reflux Ratio Separation Y icld ppm ppm Efficiency means 20 comprises an outer cylindrical member 42 I The first five examples were carried outirna colu mn concentrically positioned about inner cylindrical memsystem having a l2-inch purification zone, while the her 44 so as to form annular heating passage 46 belast two examples were carried out in a column system tween heatin fluid inlet ort 48 and heating fluid outhaving a 6-inch purification zone. The other dimensions and the displacement and rotation data are as set forth hereinabove in connection with the description of the apparatus. I

.It has been found from analysis of comparative data obtained from the apparatus of the invention and that of the prior art that, the use of a dense crystal bed in the column of the apparatus of the invention prevents backmixing in the liquid phase and allows the use of shorter column lengths than must be employed in the highly backmixed prior art apparatus.

I claim:

1. Process for the purification of multi-component feed material having a crystallizable component comprising: providing spaced freezing and melting zones, each of said zones being jacketed, a purification zone intermediate of said freezing and melting zones, and -porous piston means positioned and operative to displace crystalline phase material from said freezing zone to said purification zone; introducing liquid feed'material into said purification zone; maintaining tempera- 4 ture balance on both said freezing and melting zones to produce a controlled reflux rate of crystallizable component through said purification zoneiseparating said crystalline phase material from the other liquid phase components of said multi-component liquid feed in said purification zone; and withdrawing highly purified crystallizable component from said melting zone and the other components of said multi-component liquid from said freezing zone.

2. Process in accordance with claim 1, wherein said controlled reflux rate of crystallizable component through said purification zone is maintained so as to provide total reflux. 4

3. Process for continuous purification of multicomponent feed material having a crystallizable component comprising: providing spaced freezing and melting zones, each of saidzones being jacketed, a purification zone intermediate of said freezing and melting zones, and porous piston means positioned and operative to displace crystalline phase material from said freezing zone to said purification zone; continuously introducing liquid feed material into said purification zone; maintaining temperature balance on both said freezing and melting zones to produce a controlled reflux rate of crystallizable component through said purification zone; continuously separating said crystalline phase material from the other liquid phase components of said multi-component liquid feed in said purification zone; and continuously withdrawing highly purified crystallizable component from said melting zone and the other components of said multi-component liquid from said freezing zone at rates coordinated with the rate of continuous introduction of said liquid feed material and the temperature balance maintained in said freezing and melting zones. 

2. Process in accordance with claim 1, wherein said controlled reflux rate of crystallizable component through said purification zone is maintained so as to provide total reflux.
 3. Process for continuous purification of multi-component feed material having a crystallizable component comprising: providing spaced freezing and melting zones, each of said zones being jacketed, a purification zone intermediate of said freezing and melting zones, and porous piston means positioned and operative to displace crystalline phase material from said freezing zone to said purification zone; continuously introducing liquid feed material into said purification zone; maintaining temperature balance on both said freezing and melting zones to produce a controlled reflux rate of crystallizable component through said purification zone; continuously separating said crystalline phase material from the other liquid phase components of said multi-component liquid feed in said purification zone; and continuously withdrawing highly purified crystallizable component from said melting zone and the other components of said multi-component liquid from said freezing zone at rates coordinated with the rate of continuous introduction of said liquid feed material and the temperature balance maintained in said freezing and melting zones. 